1. Field of the Invention
The present invention relates to a semiconductor device, more particularly, to interconnects and contact structure of the semiconductor device.
2. Description of the Related Art
In order to prevent RC delay of a transfer signal of semiconductor devices, copper (Cu) is used as the interconnect material. In this case, an anti-diffusion metal film (barrier metal) is located between interconnect layer and an insulating film in order to prevent the copper from being diffused to the insulating film such as interlayer insulating film.
The following method of manufacturing the semiconductor device is given. A contact hole for connecting the lowermost interconnect layer and a transistor on a semiconductor substrate is formed in an interlayer insulating film. The contact hole is filled with tungsten via a contact (adhesive) layer. Extra tungsten on the interlayer insulating film is removed by CMP (Chemical Mechanical Polishing), and thereby, a contact plug is formed. An interconnect trench is formed in an interlayer insulating film further formed on the interlayer insulating film, and the interconnect trench is filled with copper via the barrier metal. By doing so, an interconnect layer is formed.
In the process of filling the contact hole with tungsten, an empty space calling a seam (void) 52 is formed as shown in FIG. 13 and FIG. 14. The cause of the case shown in FIG. 13 is because a contact hole 51 is formed into a shape of a barrel. For this reason, the opening of the contact hole 51 is closed before the contact hole 51 is filled with tungsten.
The cause of the case shown in FIG. 14 is because a contact layer 53 is thicker than other portions at the upper portion of the contact hole 51. This results from the characteristic of sputtering or CVD (Chemical Vapor Deposition) process employed in forming the contact layer 53. In this case also, the opening of the contact hole 51 is closed before the contact hole 51 is filled with tungsten, as in FIG. 13.
As seen from FIG. 13 and FIG. 14, the seam 52 is formed in the contact hole 51; as a result, the following problem arises. More specifically, the seam 52 is again opened or the diameter increases in the process of removing extra tungsten using CMP and in the RIE (reactive Ion Etching) process for forming an interconnect trench 57. As a result, a barrier metal 55 intrudes into the seam 52 when being formed, as illustrated in FIG. 15. For this reason, the barrier metal 55 is formed with a broken portion 56 in the interconnect trench 57.
If an interconnect material film (copper) is formed in the interconnect trench 57 in a state that the broken portion 56 is formed, there is the following problem. Electro-migration resistance is reduced in the interconnect layer with the broken portion 56 as the base point; as a result, high reliability is not obtained. If the film thickness of the barrier metal 55 is smaller than the opening diameter or depth of the seam 52, the problem described above remarkably appears.
Even if no seam 52 is formed, the surface of tungsten is rough; for this reason, the contact hole 51 is not fully filled. As a result, a clearance is formed. In the RIE process for forming the interconnect trench 57, the initially formed clearance further widens; for this reason, the same state as the seam is formed.